Numerous designs of passive and active automotive occupant restraint systems are known for enhancing occupant protection in the event of a vehicle impact. Passive systems such as inflatable restraints or air bags for frontal and side impacts and automatically deployed seat belt systems are known. Active seat belt systems have been used for many decades and are manually deployed by the occupant. The conventional seat belt system uses three points of connection with the vehicle structure and incorporates a lap belt section for engaging the occupant's lower torso, and a shoulder belt section for engaging the occupant's upper torso. When used, the seat belt restrains movement of the occupant in the event of a vehicle impact or rollover event. In order to enhance the comfort and convenience provided by the seat belt system, retractors are used which permit the belt webbing to be extracted from and retracted into the retractor, allowing movement of the occupant while maintaining the belt in close contact with the occupant. An inertia sensitive actuator may be used to lock the retractor spool when an impact or rollover event is detected, preventing further extraction of webbing to restrain the occupant.
Various approaches have been proposed to efficiently package the vehicle retractor assemblies. One approach utilizes a pair of seat belt retractors, one having a spool for winding and storing the lap belt portion of the webbing, and a second retractor for winding and stowing the shoulder belt portion of the webbing. Dual retractor systems are provided in certain vehicles to provide enhanced comfort and convenience for the vehicle occupants, and provides them with greater freedom of movement. This system is more widely used in luxury vehicles where the additional costs for the benefits of a dual retractor system are acceptable.
Dual retractor systems may also be used in conjunction with so-called inflatable belt systems. An inflatable seat belt system incorporates a section of the shoulder belt which has a bladder or tube which is inflated by a gas, typically by a pyrotechnic inflator, to increase its size and volume. Thus, when an inflatable seat belt is deployed, the normally narrow seat belt webbing expands significantly to reduce the contact pressure between the shoulder belt and the occupant during an impact event. Inflatable seat belts also act as a belt pretensioner by reducing belt slack. Inflatable seat belts are typically deployed using the crash sensing systems also used to deploy other inflatable restraint systems upon the detection of a vehicle impact or rollover event having predetermined dynamic characteristics.
Providing dual retractors for the seat occupants increases the cost and complexity of the restraint system. Further compounding the cost duplication of a dual retractor system is the emergence of an increasing number of sophisticated control systems for retractors. An example of such a control system is a retractor pretensioner. Retractor pretensioners cinch the seat belt webbing against the occupant, eliminating slack immediately upon the detection of a vehicle impact. Reducing the slack in the seat belt system enables the occupant's forward motion to quickly engage the seat belt to begin dissipating impact energy.
Another retractor control device presently known are so-called pre-pretensioners. These devices begin to cinch the seat belt webbing against the occupant when an imminent impact is detected but before an actual impact occurs. This detection can be provided using, for example, radar, ultrasonic, or other sensing systems which anticipate a vehicle crash event before actual impact has occurred. The implementation of these retractor control systems further increases the cost of providing such features in a dual retractor system, since these functions may be duplicated for each retractor.
A commonly available retractor control device presently found in automotive seat belt retractors is an inertia sensitive locking device, also referred to as a “vehicle sensitive” inertia actuator or a mechanical sensor. These devices utilize an excitation mass which moves in response to inertial forces or in the event of inclination of the vehicle and causes locking of the seat belt retractor when the vehicle is exposed to such conditions. These devices are provided to allow freedom of movement of the belted occupants, yet lock the retractor when a restraining effect is necessary. Mechanical inertia sensitive actuators have been in widespread use for many years. Various designs of these devices are employed. One type employs a ball mass which is displaced from a neutral nested position to a displaced position. Another design is a so-called “standing man” type which pivots in response to the inertia forces mentioned previously. Still another variation utilizes a hanging pendulum which pivots under inertial forces. In these described devices, some type of mechanical link such as a lever, paddle, or rod arrangement is used, which is acted upon by the excitation mass when it moves from its neutral position to a displaced position, to cause locking of the associated seat belt retractor spool. This can be done by having a lever which contacts the excitation mass to directly engage with ratchet teeth of the retractor spool. In other cases, a so-called servo or slave mechanical system is used in which the excitation mass sensor link moves and causes another set of mechanical couplings to move to a position where they engage the retractor spool ratchet to prevent further extraction of webbing. Another retractor control function which may be provided by an inertial sensitive actuator is a detection or signaling function, in which displacement of the excitation mass results in an electrical signal, used as an input of a vehicle safety system. In the case of a dual spool retractor, it is ordinarily necessary to provide a pair of inertia sensitive actuators, one for each retractor. As mentioned previously, this duplication of components adds cost and complexity to the combined system, and further increases the packaging volume of the retractor.